596 



B. F. Kingsbiiiy and H. D. Eeed. 



Amphiuma. 



In Amphiuma a single plate fills ttie fenestra vestibuli and is free 

 except on its cephalic end where it is fused with the ear capsule 

 which is cartilaginous. The very large stilus is articulated at its 

 distal end with the squasmosum and continuous with a process of the 

 palatoquadrate. Its relation to the facial nerve and blood vessels 

 is typical. On both inner and outer surfaces of the fenestral plate 

 there is a layer of bone (Fig. 18) which is continued for a short 



Fig. 18. Auiphiuma means, adult. C.I., canalis lateralis ; Col., columella ; 

 Sq., OS squamosum ; St.C, stilus columellse ; VII., nervus facialis. 



distance upon the base of the stilus. A distinct but not strong liga- 

 mentum hyo-columellare is present. Its diagrammatic representa- 

 tion is given in PL X, Fig. 71. 



The fenestral plate becomes narrower in its caudal third and 

 finally tapers to a point. In that portion of the ear capsule forming 

 the caudal margin of the fenestra there is a pronounced prominence 

 within which there is a continuation of the perilymphatic cavity of 

 the ear (Fig. 20). 



While complete developmental stages have not been studied, sec- 

 tions through the head of a larva soon after hatching, a transform- 

 ing individual and an adult furnish some data regarding develop- 

 ment. In the youngest larva the fenestral plate is relatively small 



